This invention relates to an access channel for use in the insertion tube of an endoscope or a borescope through which a tool can be passed through the insertion tube into the viewing region of the instrument.
An endoscope or borescope is characterized by an elongated flexible insertion tube having a viewing head at its distal end and a control housing at its proximal end. A bendable steering unit is located at the distal end of the tube immediately behind the viewing head. One or two pairs of control cables pass through the insertion tube between steering knobs at the control housing and the steering unit. The cables can be selectively displaced to bend the steering section to either direct the viewing head at a desired target or to manipulate the viewing head through tight bends or turns. The steering unit is generally placed as close as possible to the viewing head so that it can be precisely turned in the smallest amount of space.
Endoscopes and borescopes are oftentimes equipped with an access channel that spans the length of the insertion tube between the control housing and the viewing head. The access channel is typically closed at the control housing by a penetratable seal and opens outwardly through the viewing head. Accordingly, a tool mounted upon the end of an elongated flexible rod can be passed through the channel into the viewing region of the instrument where it can be directed onto a given target to carry out a desired task. In the medical field, a biopsy tool is commonly passed through the channel to secure tissue samples from remote body cavities and hence this type of channel is commonly referred to as a "biopsy channel".
It is common practice to form a biopsy channel in two lengths or sections of tubing. A first relatively stiff section is mounted inside the insertion tube between the control housing and the steering unit. A second more flexible section is operatively coupled to the first section and arranged to pass through both the steering unit and the viewing head. Both sections of the channel exhibit good lubricity and thus offer little resistance to a tool as it moves therethrough. It has been found, however, that the more flexible front section of the tube which is situated inside the steering unit of the insertion tube is sometimes subjected to severe bending and torsional stresses that can kink and/or otherwise deform the channel to restrict or close the opening. When this occurs, a tool will be unable to transcend the bend region to complete the desired task.